GB246890A - Improvements in and relating to duplicating - Google Patents

Abstract

246,890. Gestetner, D. Oct. 2, 1924. Stencils and stencilling.-Stencils, which may be employed for producing work on a large scale, e.g. posters, are prepared by the local application, by means of type, pens, brushes, &c., to the surface of a stencil sheet composed of a porous base and a layer impervious to ink including a gelatinized organic colloid such as gelatine, agaragar, starch, dextrine, carbohydrate gums, &c., of an agent adapted to liquefy or depress the gelating point of the colloid, the softened colloid being afterwards removed. Where the colloid is a protein, bodies included in the Hofmeister series, such as sulphuric acid, ammonium thiocyanate, or sodum iodide, may be employed as softening agents, and colouring matters may be associated therewith. To increase the viscosity and prevent the lateral spreading of the softening agent, substances such as carbon black, china clay, bentonite, or kieselguhr may be mixed therewith. The stencil sheet may be provided with a screen of material unaffected by the softening agent, such as a solution of celluloid, which may be sprayed to produce dots over the surface. Alternatively, the screen may be produced by printing. To remove the softened colloid, a paper sheet coated with blown rape oil may be pressed on to the stencil sheet, the softened colloid adhering thereto on removal. Preferably, the sheet bearing the softened colloid is treated with oily ink on a duplicating machine, the ink forcing its way through the softened portions and thus removing them. Where the inked portions of the stencil are of large size, the support may be of fine lawn and a brush may be used to remove the softened colloid; for finer work, Yoshino paper is employed for the base.